Ring topologies are known as network topologies for communication networks. A typical ring topology is a network configuration in which relay apparatuses including bridges and Layer 2 (L2) switches are connected in a circular pattern. Since an alternative path is ensured in the ring topology even if a communication failure occurs at part of the ring, the reliability of the communication network is improved. In the communication network adopting the ring topology (hereinafter referred to as a ring network), a block point at which a frame that circles around is discarded is known in order to avoid the circling of a frame the destination of which is unknown.
Use of a virtual local area network (VLAN) is also known in the ring network described above. The VLAN is a technology to virtually realize multiple communication networks even in one physical communication network by including an identifier for identifying each VLAN in a frame. The VLAN allows the relay apparatuses composing the ring network to be effectively used.
In the ring network using the VLANs, a technology to set the block point for each VLAN and select the VLAN having a communication path of a minimum number of hops as an optimal communication path is also known (for example, refer to Japanese Laid-open Patent Publication No. 2006-261806).
When, for example, a frame the destination of which is unknown enters the ring network using the VLANs, the frame basically circles around all the relay apparatuses until the frame is discarded at the block point set for each VLAN. However, only one communication path is allocated to the VLANs having the same identifier on the ring and only one user is capable of using the communication path. The maximum number of the identifiers of the VLANs is defined by The Institute of Electrical and Electronics Engineers, Inc. (IEEE) 802.1Q. Accordingly, the increase in the number of identifiers may cause the ring network using the VLANs not be realized.